Step 1: Overview of Down syndrome.
Down syndrome is a genetic disorder caused by trisomy of chromosome 21. It is associated with a variety of physical, developmental, and physiological abnormalities.
Step 2: Characteristic symptoms.
Common symptoms of Down syndrome include:
Heart defects, such as heart murmurs.
Flattened facial profile and upward slanting eyes.
Intellectual disability and developmental delays.
Step 3: Analysis of options.
Option (A): Incorrect. Abnormal hair growth is not a characteristic symptom.
Option (B): Correct. Heart murmurs are commonly associated with congenital heart defects in individuals with Down syndrome.
Option (C): Incorrect. Skin rash is not a typical symptom.
Option (D): Incorrect. Eye color changes are unrelated to Down syndrome.
\[
\therefore \text{The correct answer is: Heart murmurs.}
\]